The present invention relates to a discharge lamp lighting apparatus and a lighting appliance employing the same for lighting the discharge lamp in which an inert gas-dominated discharge agent is filled.
The inert gas discharge lamp has an advantage of a luminous flux start-up property at a low temperature since in the inert gas discharge lamp the phosphor is emitted by an ultraviolet radiation which is generated by the inert gas discharge and the luminous energy does not depend on the temperature. However, it also has a drawback that the luminous efficiency is lower than that of a mercury-vapor discharge lamp.
On the other hand, the discharge lamp which radiates a visible light by the fluorescent substance layer excited by the ultraviolet radiation generated by the inert gas discharge is improved the luminous efficiency by pulsive-lighting is described in the Japanese Patents, Tokkai-sho 58-135564, Tokkai-Hei 2-174097, Tokko-Hei 8-12794, and Tokkai-Hei 9-199285.
Further, a discharge lamp lighting apparatus having such effects those of the prior arts by applying a high frequency AC voltage whose waveform is adjusted by superposing DC voltages so that a lamp current having a pause period flows across a pair of the electrodes of the discharge lamp, at least one of which is placed on the outer surface of the discharge vessel, is also proposed.
By the way, since a discharge lamp having a pair of the electrodes, in which at least one of the electrodes is placed on the outer surface of the discharge vessel, uses a dielectric barrier discharge, there is a tendency of that generally a starting voltage and a lamp voltage become very high.
Accordingly there is a problem that a high frequency generator breaks down due to the high voltage generated by the high frequency generator itself, if the high frequency generator keeps on operating at a no-loaded state. Further, the insulation of the discharge lamp, a harness wire for feeding power, or a high voltage part of the high frequency generator are easy to be breakdown since the above-described high voltage is applied. When the insulation has been breakdown, it progresses to a serious problem of causing an abnormal discharge.
On the other hand, in the dielectric barrier discharge lamp, it is supplied with a power of a high voltage and a high frequency. Therefore, an abnormal discharge at a high voltage and a high-frequency in different from those of normal discharge occurring between a pair of electrodes in a discharge vessel is relatively easy to occur, even when it is not in a no-load state. Such an abnormal discharge may occur in any of an electrode, a high frequency generator, and a harness connecting the electrode and the high frequency generator with each other. Abnormal discharge at an electrode may also occur in any of between different polarity points and between same polarity points. Abnormal discharge between different polarity points occurs, for example, along the external surface of a discharge vessel. The abnormal discharge between same polarity points occurs in such a case that there is a crack on one electrode. Abnormal discharge at the harness occurs in such as a case when the insulation of the harness is damaged. Abnormal discharge in a high frequency generator occurs in such cases that there are an insulation degradation of an output transformer, an insulation degradation of a high voltage pattern on a printed-wiring board, and a crack or a poor contact at a soldering of a high voltage pin of an output connector.
Once such an abnormal discharge has been occurred, an abnormal discharge occurring region will evolve heat. As a result, there is a danger of that a smoking or a firing may occur at the discharge lamp, the harness, or the high frequency power supply. Furthermore, by such abnormal discharges the near-by materials of abnormal discharge occurring region is degraded, or potentially causes a smoking or firing. Such a smoking or firing must be prevented before it happens.
On the other hand, the Japanese Patent Application Tokkai 2001-15827 which was filed before the present application, but published after the publication of the original application of the present application discloses a technology in that an abnormal discharge detection circuit is provided in a dielectric barrier discharge lamp device for detecting the abnormal discharge based on an electrical behavior of a power supply so as to suspend feeding of a high voltage AC current from the power supply to the dielectric barrier discharge lamp device. However, it is not a particular technology to detect an abnormal discharge of a discharge lamp based on such an electrical behavior of the power supply. By the way, if taking note on FIG. 7 and its associated description in the Tokkai 2001-15827, there is disclosed a circuitry for exclusively extracting the high frequency components 31 in the output amount detection signal detected upon an abnormal discharge so as to suspend the power supply.
That is, the circuitry of the Tokkai 2001-15827 has a resistor 120 for detecting a discharge current connected in series a dielectric barrier discharge lamp and a high pass filter 29 for exclusively extracting the high frequency components 31 in the output amount detection signal detected upon an abnormal discharge from a voltage drop across the resistor 120. The circuitry has a diode 124 for rectifying the high frequency components 31 outputted from the high pass filter 29, and an integrator comprised of a capacitor 125 and a resistor 126 for integrating the rectified output so as to extract a fluctuation 34 of the high frequency components 31. The circuitry also has a comparator 87 for comparing the fluctuation 34 of the output amount detection signal with a preset fluctuation limit 36. When the fluctuation 34 is higher than the limit 36, a low level signal 18 which indicates that an abnormal state has been detected is applied to a latch circuit 127. The latch circuit 127 generates and then holds a low level latch signal in response to the low level signal 18. In this state, since the output of the comparator 57 cannot pass through a gate 119, a power supply comes to be suspended.
Also disclosed in FIG. 5 and its associated description of the Tokkai-2001-15827, a circuitry which detects an output voltage of a voltage boosting type chopper DC source 49 for feeding a push-pull type inverter to produce a chopper output voltage signal 52, and suspends the chopper DC source 49 when the chopper output voltage signal 52 has been off the upper or lower limitation preset for the push-pull type inverter.
That is, the device of the Tokkai 2001-15827 detects an output voltage of the voltage boosting chopper type DC power supply 49 by the diode 50 and capacitor 51, and generates the chopper output voltage signal 52. When an excessive electric power has been consumed due to the abnormal discharge and the like, the chopper output voltage signal 52 fails to reach a target defined by a dividing ratio according to two resistors 101 and 102. In this occasion, the primary clock signal 63 is suspended and thus the power supply is also suspended. Furthermore, in a case of the abnormal discharge whereat a target power fails to be consumed, the primary clock signal 63 fails to be generated, and thus the power supply is also suspended.
Furthermore, the Tokkai-2001-15827 describes that the circuitry of FIG. 5 may further incorporate therein the resistor 120, the diode 121 and the abnormal discharge detection circuit 14, as shown in FIG. 7, so that it is possible to deactivate a transistor 106 when the output of the comparator 27 is in a low level, too.
1: Disadvantages in the circuitry of FIG. 7 and its associated descriptions of the Tokkai 2001-15827:
The circuitry can carried out a protection operation if an abnormal discharge is developed even in a no-load state. However, since the protection operation is carried out after that the insulation of the harness, or the high frequency generator had been damaged, not only the protection operation is uneconomical, but also the risk is too high. Moreover, when an abnormal discharge occurs during the discharge lamp works, the device of the Tokkai 2001-15827 is difficult to carry out a sufficient protection. This is because the device of the Tokkai 2001-15827 is constructed to compare the fluctuation 34 of the output amount detection signal with the preset fluctuation limit 36 by the comparator 87, and then carries out the protection operation at only when the fluctuation 34 of the output amount detection signal is higher than the fluctuation limit 36. Therefore, in the device of the Tokkai 2001-15827 when a minute abnormal discharge current flows the fluctuation 34 of the output amount detection signal becomes small and thus fails to exceed the fluctuation limit 36 and thus fails to carry out the protection operation. By the way, according to an afterthought of the Tokkai 2001-15827, it would be possible to think that the fluctuation limit 36 of the output amount detection signal is free to be brought closer and closer to zero. However, it is clear that such a thought is far from the design concept of the Tokkai 2001-15827, and thus the thought is too formidable. Furthermore, as the device of the Tokkai 2001-15827 integrates the output of the HPF 29 by the integrator comprised of the capacitor 125 and the resistor 28 after that it has been rectified in the diode 124, there is a disadvantage of that the protection operation will be lagged due to the time constant of the integrator.
On the other hand, there is a case that a minute abnormal discharge current may flow in similar to the case of the abnormal discharge occurring between the said polarity points. Since this type of abnormal discharge also has the risk of smoking or firing, it is necessary to carry out a protection operation in similar to the case where a large abnormal discharge current flows.
2: Disadvantages in the circuitry of FIG. 5 and its associated descriptions of the Tokkai 2001-15827:
Although the circuitry is able to detect an overload state and a low load state since it detects a DC output voltage of the voltage boosting type chopper DC source 49 to produce the chopper output voltage signal, it fails to exclusively detect the abnormal discharge. Therefore, since the circuitry of the Tokkai 2001-15827 fails to distinguish a dimming or a high output lighting of the discharge lamp from the abnormal discharge, the circuitry will uniformly suspend the power supply in any case of them. For this reason, the circuitry of the Tokkai 2001-15827 cannot satisfy the demand of lighting a discharge lamp at a various modes.
3. Disadvantages in the circuitry of FIG. 5 of the Tokkai 2001-15827 which integrates therein a part of FIG. 7:
This circuitry is of detecting an abnormal discharge by using two detectors in parallel to carry out a detection operation. Therefore, not only the circuitry is complicated, but also the afore-mentioned disadvantages exist together, without resolved. Thus, the circuitry still fails to correctly detect and protect the abnormal discharge.
The present invention has an object to provide a discharge lamp lighting apparatus and a lighting appliance employing the same which is able to not only quickly protect against an abnormal operation, but also automatically return to the normal operation when the cause of the abnormal operation has been dissolved.
In particular, the present invention has an object to provide a discharge lamp lighting apparatus and a lighting appliance employing the same which is able to not only quickly protect against a no-load, but also automatically return to a normal operation when the no-load has been dissolved by placing the discharge lamp normally.
Further, particularly, the present invention has an object to provide a discharge lamp lighting apparatus and a lighting appliance employing the same which is able to protect against a weak abnormal discharge, but also automatically return to a normal operation when the abnormal discharge has been dissolved by exchanging the discharge lamp.
Further, particularly, the present invention has an object to provide a discharge lamp lighting apparatus and a lighting appliance employing the same which is able to not only quickly protect an overcurrent, but also automatically return to a normal operation when the overcurrent state has been dissolved.
A discharge lamp lighting apparatus according to a first aspect of the present invention includes, a discharge lamp provided with a discharge vessel filled with an inert gas-dominated discharge agent and a pair of electrodes at least one of which is placed on the outer surface of said discharge vessel, a high frequency generator provided with a switching device for generating a high frequency voltage with a high frequency switching operation and an output transformer for outputting the high frequency voltage, for lighting the discharge lamp by supplying to the discharge lamp through a pair of electrodes with the high frequency voltage induced across a secondary winding of said output transformer, a high frequency operation detector for detecting at least one of the high frequency voltage and the high frequency current and thus producing a high frequency operation detection signal, a controller for controlling said switching device of the high frequency generator in a feedback manner for a normal operation state in response to the high frequency operation detection signal applied thereto so that the high frequency operation detection signal becomes around a first level in a normal operation state, while carrying out a protection operation when the high frequency operation detection signal applied thereto has changed to a second level, and a no-load detector for detecting a no-load condition of the secondary winding of the output transformer and forcefully changing the high frequency operation detection signal supplied to the controller to the second level.
This aspect of the invention defines a configuration for detecting the no-load condition and carrying out the protection.
In the following descriptions, some definitions and their technical meanings are presented for following specific terms, unless otherwise specified.
The discharge lamp is provided with at least a discharge vessel, a discharge agent and a pair of electrodes. At least one of the electrodes is placed on the outer surface of the discharge vessel and the inert gas-dominated discharge agent filled in the discharge vessel. Thus the discharge lamp has a configuration for inducing a so-called dielectric barrier discharge.
The discharge vessel can be made of any dielectric material if limited in that the material has a sealing performance and heat-resistance at a working temperature. However discharge vessel is typically made of a soft glass, a hard glass or a semi-hard glass. In case of a discharge lamp wherein a visible radiation is used for lighting, the discharge vessel is enough to exclusively transmit the visible radiation therethrough. While, in case of a discharge lamp wherein an ultraviolet radiation is used for lighting, a discharge vessel such as a silica glass etc. having an ultraviolet radiation transmission property can be used for the discharge vessel. Herein the term xe2x80x9clightingxe2x80x9d means whole the things of using radiations from discharge lamps.
Here, the shape of the discharge vessel is not limited. That is, the discharge vessel may have any shape required in response to the application of the lighting. For example, the discharge vessel may be a tubular one, a planer one and the like. Further, the term xe2x80x9ctubularxe2x80x9d means either of a straight-shape tube and a bent-shape tube. Further, the bent-shape may be a toroidal shape, a semi-toroidal shape, a U-letter shape, a W-letter shape, a saddle-shape or a spiral shape. Furthermore, in case of a tubular shape discharge lamp, the size and the length of the tubular shape can be arbitrarily designed in accordance with a practical usage.
The discharge agent is dominated by an inert gas. Although xenon is preferable for the inert gas, it is also possible use any one of or a mixture of two or more of krypton, argon, neon and helium for the inert gas. Here, the term xe2x80x9cinert gas-dominated discharge agentxe2x80x9d allows that the discharge agent contains a halogen in addition to the inert gas which dominates in the discharge agent.
In a pair of electrodes, at least one of the electrodes is placed on the outer surface of the discharge vessel. Hereinafter, the electrode placed on the outer surface of the discharge vessel is referred to as an outer electrode, and the other electrode placed in the discharge vessel is referred to as an inner electrode, for the sake of convenience. As an arrangement of a pair of the electrodes, there are two options available. That is, in one arrangement two electrodes may be provided as outer electrodes. While in another arrangement one electrode may be provided as an outer electrode and the other electrode may be provided as an inner electrode. When at least one of the electrodes is provided as the outer electrode, a capacitance presents between two electrodes facing each other via the wall of the discharge vessel as a dielectric. Thus a dielectric barrier discharge may be induced due to such a construction.
The outer electrode is placed on or almost in touch with the outer surface of the discharge vessel. The outer electrode is preferably made of a conductive thin film. As such a conductive thin film, a conductive metal foil such as an aluminum foil, a silver foil and a copper foil, a conductive metal film evaporated on a light-transmissive plastic sheet, a metalized film, a conductive metal film, a conductive paste film prepared by a screen printing technique, an ITO film, an NESA film etc. are available. When forming the outer electrode by a conductive thin film, it may be shaped into a ribbon, or may have a hetero-shape such as a wave shape. The actual condition of the outer electrode is not limited to the conductive thin films. For example, if needed, the outer electrode may be a coil, a mesh etc. made of conductive material and be placed on or almost in touch with the outer surface of the discharge vessel. Here, the term xe2x80x9cplaced . . . almost in touch with . . . xe2x80x9d means that although it is preferable that the whole of the outer electrode is placed in touch with the outer surface of the discharge vessel, it is not an indispensable condition and that all in all the outer electrode may be placed in touch with the outer surface of the discharge vessel. Further, the outer electrode is able to have a size that at least a part of the outer electrode may extend in the longitudinal or axial direction of the discharge vessel. And in the circumferential direction of the discharge vessel the outer electrode may extend all around the discharge vessel or within a limited arc range along the discharge vessel.
Furthermore, if the outer electrode is worked into a coil or a mesh, or made of light-transmissive conductive film, such an electrode allows the light emitted in the discharge vessel be derived outside through the outer electrode. Thus such an outer electrode can be placed all around the discharge vessel. On the other hand, if the outer electrode made of metal foil is used, the metal foil is affixed in advance to the one side of a light-transmissive plastic sheet as described later in detail, and then the light-transmissive plastic sheet is stuck at its other side on the outer surface of the discharge vessel with adhesive coated on the other surface of the light-transmissive plastic sheet. However it is also possible to directly stick a metal foil on the outer surface of the discharge vessel. Further, the width of the outer electrode may vary in the axial direction of the discharge vessel.
Next, to make the outer electrode contact with the outer surface of the discharge vessel an adhesive is coated in advance on a mating surface of the outer electrode, the outer electrode is adhered to the discharge vessel with the adhesive. However, it is also possible to coat an adhesive on a surface of the discharge vessel to be mated with the outer electrode and then affix the outer electrode on the surface to be mated. Further, it is also possible to just put the outer electrode on the discharge vessel without using any adhesive, and then wrap a light-transmissive plastic sheet coated with an adhesive all round the discharge vessel.
Now an arrangement of the pair of the electrodes to the discharge vessel will be described. As to the arrangement of the pair of the electrodes there are a variety of type as described below, and any type can be arbitrarily selected from them.
A pair of electrodes may be placed either inside or outside the discharge vessel if at least one of them is placed so that a discharge occurs inside the discharge vessel in the aid of a discharge agent.
1. Inner and outer electrodes arrangement:
This type of arrangement includes a set electrodes comprised of one or more inner electrodes and one or more outer electrodes. This type of arrangement is further divided into two types, i.e., a type of the inner electrode having a short-length and a type of the inner electrode having a long-length extending along the longitudinal direction of the discharge vessel.
(1) Electrodes arrangement including short-length inner electrode:
In this electrodes arrangement, there is used a short-length inner electrode which is similar to the electrode used in conventional inner-electrode type fluorescent lamps.
(1-1) Electrodes arrangement wherein single inner electrode is placed on one end of discharge vessel and single outer electrode is placed on outer surface of discharge vessel:
(1-2) Electrodes arrangement wherein a pair of inner electrodes are placed on both ends of discharge vessel and single outer electrode is placed on outer surface of discharge vessel:
In this electrode arrangement (1-2), a pair of inner electrodes are commonly connected to one terminal of lighting circuits and the outer electrode is connected the other terminal, or a pair of inner electrodes are separately connected to each one terminal of a pair of lighting circuits and the outer electrodes are commonly connected to the other terminals at the same potential.
(1-3) Electrodes arrangement wherein a pair of inner electrodes are placed on both ends of discharge vessel and a pair of outer electrodes are placed on outer surface of the discharge vessel:
In this electrode arrangement (1-3), inner electrode and outer electrode face each other in one-to-one correspondence.
(1-4) Electrodes arrangement wherein three inner electrodes are placed on both ends and in the middle of the discharge vessel and single long-length outer electrode faces them in common:
(1-5) Electrodes arrangement wherein three inner electrodes are placed on both ends and in the middle of the discharge vessel and three outer electrodes are placed on the outer surface of the discharge vessel in respectively facing with the inner electrodes:
(2) Electrodes arrangement including long-length inner electrode:
In this electrodes arrangement, there is used a long-length inner electrode extending over the substantial whole length of the discharge vessel.
In this electrodes arrangement, there are two types. One is that both ends of the inner electrode are exposed outside the discharge vessel by hermetically passing through the ends of the discharge vessel. The other is that one end of the inner electrode is exposed outside the discharge vessel by hermetically passing through one end of the discharge vessel, and the other end of the inner electrodes is placed inside the discharge vessel in proximity to the other end of discharge vessel.
2. Outer electrodes arrangement:
In this electrodes arrangement, the pair of outer electrodes are placed on separated portions of the outer surface of a discharge vessel in facing with each other across discharge vessel. As to the outer electrodes, a pair or plural pairs of them can be arranged along the longitudinal direction of the discharge vessel. Here, in a so-called aperture type discharge vessel, the outer electrodes must be placed on positions where they do not substantially block the light emission through the aperture.
Although such a fluorescent substance layer is not indispensable for the discharge vessel of the present invention, the fluorescent substance layer can be formed on the inner surface of the discharge vessel as needed. The fluorescent substance may be freely selected from a variety of known fluorescent substances according to practical usages of discharge lamps. For example, in a color scanner usage, a three band emission fluorescent substance can be used. Further, in a monochrome scanner usage, a green-light emission fluorescent substance can be used. Here, the term xe2x80x9cthe fluorescent substance layer can be formed on the inner surface of the discharge vesselxe2x80x9d means that not only the fluorescent substance layer can be directly formed on the inner surface of the discharge vessel, but also the fluorescent substance layer can be formed on a guard film which is formed in advance on the inner surface of the discharge vessel.
A high frequency generator is an apparatus for inducing a dielectric barrier discharge by supplying a high frequency energy with desirable voltage and power to the discharge lamp. Further, limited only by a switching device for generating a high frequency voltage by switching operation at a high frequency and an output transformer for outputting the high frequency voltage so as to supply to the discharge lamp through a pair of electrodes with the high frequency voltage induced across a secondary winding of the output transformer in order to drive lighting of the discharge lamp, other configurations are not limited in the high frequency generator. Here, in this application, the term xe2x80x9chigh frequencyxe2x80x9d means a frequency of 1 kHz or higher, or more preferably, a frequency of about 4 to 200 kHz. The high frequency generator can be provided with a resonant circuit for generating a sinusoidal-wave current, as needed. In this case, the resonant frequency is set to a value higher than an operation frequency for operating stably in a phase-lag range. For example, when the operation frequency is 70 kHz, the resonant frequency us set at around 500 kHz. The high frequency energy to be supplied to the discharge lamp would be either of a pulse wave or a continuous wave. Here, the term xe2x80x9ccontinuous wavexe2x80x9d means that positive states and negative states alternate in succession without a pause period. The positive states and the negative states may be either of symmetrical or asymmetrical in the continuous wave. For instance, by superposing harmonics on a fundamental sine-wave, the rising edge and the lowering edge of the voltage waveform can become relatively steep. Or by superposing a DC voltage on a fundamental sine-wave, the continuous wave may become asymmetrical. When a high frequency AC voltage is so adjusted that the lamp current having an enough pause period flows the lamp, it is possible to induce an afterglow in the discharge lamp during the pause period of the lamp current the same as the case of applying pulse voltage.
An inverter or a switching regulator is generally used as a circuit for generating high frequency. However, the circuit is not limited to such ones. For example, the high frequency generator could be comprised of an oscillator and a power amplifier.
The output transformer isolates the DC conduction between the primary winding and the secondary winding. The transformer may include a tertiary winding, additional primary windings or additional secondary windings further to the fundamental primary and secondary windings. Further, since the discharge lamp induces the dielectric barrier discharge by applying across the pair of electrode with a voltage induced across the secondary winding of the output transformer, it is necessary to raise the voltage induced in the secondary winding. Accordingly, it is preferable that the output transformer is a voltage boosting type. However the output transformer can be a voltage lowering type or a voltage equalizing type, if required.
The switching device operates to generate a high frequency by a switching operation. As the switching circuit, a proper circuit such as an inverter or a switching regulator can be employed, if desired. As a result, one or a plurality of switching devices can be used according to a circuit system. Further the switching device is able to use a semiconductor switch such as a MOSFET or a bipolar transistor.
The high frequency operation detector is an apparatus for yielding a high frequency operation detection signal as a feedback signal for making feedback control the switching device of the high frequency generator so as to generate a stable high frequency voltage from the high frequency generator. The signal format of the high frequency operation detection signal is determined according to the type of the feedback control. That is, in a constant-voltage-control mode a high frequency voltage is detected. In a constant-current-control mode, a high frequency current is detected. While, in a constant-power-control mode, both the high frequency voltage and the high frequency current are detected. Any of the high frequency voltage and the high frequency current can be detected at the primary side or the secondary winding of the output transformer. Here, since the high frequency voltage is detected by typically using a boosting transformer, when considering a miniaturization of the transformer it is better to make the detection at the primary side of the output transformer.
When the high frequency voltage and the high frequency current are detected by controlling the constant power, they may be detected independently, or they may be commonly detected by using single detection circuit. Here, as an actual configuration of the detection circuit a variety of known devices could be used without being specifically limited.
Controller controls a feedback control and a trouble-shooting. The feedback control is applied for the switching operation of the switching device which makes the high frequency means to generate a high frequency during a normal operation. The latter control, i.e., the trouble-shooting is a protection for the switching operation of the switching device at an abnormal time. A section making the feedback control and a section making the trouble-shooting could be independently constructed. Or they could be so constructed that they are centrally controlled, by being comprised of an IC such as a switching regulator IC as its key component.
Further, the controller makes a feedback control during normal operation in that the high frequency operation detection signal is in the first level. The feedback control is an operation for keeping a voltage, a current or a power in constant by controlling the switching operation of the switching device in a PWM control fashion, a frequency control fashion or a voltage control fashion by means of feeding back the voltage, the current or the power of the high frequency output for driving a discharge lamp. Further the controller makes a prescribed protecting operation during abnormal operation wherein the high frequency operation detection signal takes a second level. Here, the term xe2x80x9cfirst levelxe2x80x9d means any level other than a second level as mentioned later. Further, the term xe2x80x9cprotecting operation controlxe2x80x9d means an action of controlling protecting operations for preventing danger due to an abnormal discharge, such as suspending the high frequency generation, making intermittently the high frequency generation or making the high frequency generation at a lowered voltage. Furthermore, the term xe2x80x9cabnormal timexe2x80x9d means principally the time that the high frequency generator operates in a no-load condition.
The controller could be configured to suspend the protecting operation for a predetermined time at the starting of the discharge lamp. Since in this sort of discharge lamp an extremely high voltage is applied thereto on starting, and also an abnormal discharge differing from a primary discharge occurring through a discharge agent is apt to occur for a short time, it is able to carry out a reliable protecting operation by avoiding a transient time such as the starting time.
A no-load detector detects a no-load condition of the secondary winding of the output transformer. In addition, it forcefully changes the high frequency operation detection signal which is supplied to the controller into the second level. Whether the secondary winding of the output transformer is in the loaded state or the unloaded state during the operation of the high frequency generator is possible to be detected either by the voltage or the current on the secondary side of that the output transformer or the by the condition such as the temperature or the light of the discharge lamp which is loaded. In this aspect of the invention, any of them can be used for the detecting operation.
The high frequency operation detection signal supplied to the controller when the no-load condition is detected is forcefully changed to the second level by lowering the level of the high frequency operation detection signal such as shorten or cut off one part or entire part of the high frequency operation detection signal in the high frequency operation detector with a switch. On the contrary, the level could be increased by increasing the high frequency operation detection signal. That is, the term xe2x80x9csecond levelxe2x80x9d is a level that is electrically judicable and apparently different from one of the high frequency operation detection signal during normal operation.
In this aspect of the invention, when the no-load detector detects the no-load condition on the secondary winding of the output transformer, it forcefully changes the high frequency operation detection signal which is supplied to the controller from the first level to the second level, so as to control the switching device for generating high frequency in the high frequency generator to carry out protecting operation. Accordingly, it is possible to speedily carry out a suitable protecting operation.
Further, since the protecting operation is carried out by forcefully changing the level of the high frequency operation detection signal to be supplied to the controller so that the signal is used for the feedback control during normal operation, the discharge lamp lighting apparatus will be simple in its circuitry and comparatively less-expensive.
The discharge lamp lighting apparatus according to a second aspect of the invention is comprised of, a discharge lamp provided with a discharge vessel filled with an inert gas-dominated discharge agent and a pair of electrodes at least one of which is placed on the outer surface of said discharge vessel, a high frequency generator provided with a DC supply, an output transformer connected across the terminals of the DC supply and a switching device connected in series with the primary winding of the output transformer for constituting a primary side circuit, a high frequency operation detector for generating a high frequency operation detection signal by detecting at least one of a high frequency voltage or a high frequency current on a primary winding of the output transformer, a controller comprised of a regulator IC with a shutdown function for controlling said switching device of the high frequency generator in a feedback manner for a normal operation state in response to the high frequency operation detection signal applied thereto so that the high frequency operation detection signal becomes approximately a first level, while controlling the switching device of the high frequency generator so as to carry out a protection operation by operating the shutdown function when the high frequency operation detection signal has changed to a second level, and a no-load detector for detecting a lamp current flowing through the discharge lamp and also for changing the high frequency operation detection signal supplied to the controller to be the second level when the lamp current is not detected.
This aspect of the invention defines a configuration for making protecting operation by detecting a no-load condition in similar to the first aspect of the invention.
The high frequency generator is provided with a DC power source, an output transformer and a switching device. The DC power source may be either of an AC-to-DC rectified power source which rectifies an AC power into a DC power or a battery. The switching device generates a high frequency by switching the DC voltage at a high frequency. The output transformer Transmits a high frequency energy from the primary side to the secondary side with an isolation of DC conduction between the primary side and the secondary side.
The controller is comprised of a regulator IC with a shutdown function. The shutdown function acts at a time that the high frequency operation detection signal has moved to the second level. Accordingly, the regulator IC is able to make a feedback control during the normal operation and the protecting operation control during the abnormal operation of the switching device.
The no-load detector is an apparatus for detecting a no-load condition by detecting a lamp current flowing through the discharge lamp at the secondary winding of the output transformer. For detecting the lamp current, it is able to adopt a variety of known techniques such as detecting of a voltage drop across an impedance element or a current transformer connected in series with the discharge lamp.
This aspect of the invention employs the regulator IC with a shutdown function for the main part of the controller. Since the shutdown function suspends generation of the high frequency to carry out the protection operation, the circuitry is free from any hunting associated with the control. Moreover, the control becomes exact and the response becomes faster. In addition, a circuit assembly becomes simplified.
Moreover, since this aspect of the invention is able to detect the non-load state based on a lamp current, it is able to accomplish a superior accuracy of detection and a simple circuitry. Other operations and effects are the same as those of the first aspect of the invention.
A discharge lamp lighting apparatus according to a third aspect of the invention includes, a discharge lamp provided with a discharge vessel filled with an inert gas-dominated discharge agent and a pair of electrodes at least one of which is placed on the outer surface of said discharge vessel, a high frequency generator provided with a switching device for generating a high frequency voltage with a high frequency switching operation and an output transformer for outputting a high frequency voltage, for lighting the discharge lamp by supplying to the discharge lamp through a pair of electrodes with the high frequency voltage induced across a secondary winding of said output transformer, a high frequency operation detector for detecting at least one of the high frequency voltage and the high frequency current and thus producing a high frequency operation detection signal, a controller comprised of a regulator IC with a shutdown function for controlling said switching device of the high frequency generator in a feedback manner for a normal operation state in response to the high frequency operation detection signal applied thereto so that the high frequency operation detection signal becomes around a prescribed level, while controlling the switching device so as to carry out a protection operation by operating the shutdown function when an abnormal discharge control signal has been applied thereto, and an abnormal discharge detector provided with an abnormal discharge current bypass wherein an abnormal discharge current flowing through the secondary winding of the output transformer is bypassed and a control switch for controlling the switching device to carry out protection by an abnormal discharge control signal applied to the controller of the switching device when a prescribed abnormal discharge current flows through said abnormal discharge current bypass.
This aspect of the invention defines a configuration for carrying out a protecting operation by detecting an abnormal discharge.
The controller is comprised of a regulator IC with a shutdown function. For this reason, the controller is provided with a shutdown terminal. When the abnormal discharge control signal as mentioned later is applied to the shutdown terminal, a shutdown function operates to control the switching device of the high frequency generator and then suspend the high frequency generating operation. Therefore, the Regulator IC carries out a feedback control at the normal operation of the switching device, and the protection operation when an abnormal discharge has occurred.
If an abnormal discharge occurs upon lighting of the dielectric barrier discharge lamp, an abnormal discharge current with a pulse rising edge (pulse falling edge) steeper than that of a normal lamp current and a peak value larger than that of the normal lamp current flows. In the high frequency output current of the high frequency generator at the time higher order harmonics are superposed on the pulse rising edge (pulse falling edge). These harmonics have a frequency of 50 MHz or more. Here, the term xe2x80x9cabnormal dischargexe2x80x9d means a several aspects of discharge phenomena, as principally described below.
1. A discharge occurring between two electrodes placed on the outer surface of the discharge vessel,
2. A discharge occurring between two electrodes due to a breakdown of an insulation of a harness wire for feeding power,
3. A discharge occurring between two electrodes due to a crack of soldering to a high-voltage output connector pin of the high frequency generator,
4. A discharge occurring between two electrodes due to a deterioration of an high-voltage output pattern on a print circuit board of the high frequency generator;
5. A discharge occurring between two electrodes due to an insulation deterioration of the output transformer in the high frequency generator;
6. A discharge occurring around a break broken in the middle of the outer electrode; and
7. A discharge occurring between an outer electrode and its terminal-lead.
In this aspect of the invention, the abnormal discharge detector is provided with an abnormal discharge current bypass and a control switch.
A bypass circuit bypasses the higher order harmonics component of abnormal discharge current flowing through the secondary winding of the output transformer. As a result, only the steep pulse rising edge of the abnormal discharge current, i.e., the higher order harmonics current is selected. For the bypass circuit for bypassing the higher order harmonics current, a high pass filter which passes therethrough frequency components of, e.g., 50 MHz or more can be employed. Moreover, the bypass circuit generates an abnormal discharge detection signal, upon detecting an abnormal discharge current.
The switching device carries out a switching operation based on an abnormal discharge detection signal to generate an abnormal discharge control signal. This abnormal discharge control signal is applied to the shutdown terminal of a controller. This control signal calls a shutdown protection operation for the controller.
In this aspect of the invention, when an abnormal discharge has occurred, the abnormal discharge current bypass bypasses the abnormal discharge current. The control switch then detects the bypass current. Following the bypass current detection, the control switch then calls a protecting operation for the controller of the switching device by supplying the abnormal discharge control signal thereto. Accordingly, as the controller shuts down the switching operation of the switching device, the high frequency generator quits its operation of generating the high frequency. Thus the protecting operation is carried out.
As will be understood from the above description, in this aspect of the invention the bypass circuit exclusively bypasses, once an abnormal discharge has occurred, a higher order harmonics current to generate an abnormal discharge detection signal regardless of the lamp current, unlike the operation of the circuitry of the Tokkai 2001-15827 to detect an abnormal discharge when the fluctuation is higher than a preset limit. That is, even a minute abnormal discharge occurring between the said polarity points, it is quickly detected. Since the switching produces the abnormal discharge control signal in response to an abnormal discharge detection signal, it is able to quickly carry out the protection operation.
As this aspect of the invention exclusively detects an abnormal discharge regardless of the lamp current of the discharge lamp, if the discharge lamp is lighted at a low power for dimming the discharge lamp or lighted at a high power, the abnormal discharge detector operates without malfunction. Therefore, since the discharge lamp can be lighted in the various modes, this aspect of the invention is adaptable for wide applications.
As the controller is comprised of a regulator IC with a shutdown function, and since the shutdown function suspends generation of the high frequency to carry out the protection operation, the circuitry is free from any hunting associated with the control. Moreover, the control becomes exact and the response becomes faster. In addition, a circuit assembly becomes simplified.
A discharge lamp lighting apparatus according to a fourth aspect of the invention includes, a discharge lamp provided with a discharge vessel filled with an inert gas-dominated discharge agent and a pair of electrodes at least one of which is placed on the outer surface of said discharge vessel, a high frequency generator provided with a switching device for generating a high frequency voltage with a high frequency switching operation and an output transformer for outputting a high frequency voltage, for lighting the discharge lamp by supplying to the discharge lamp through a pair of electrodes with the high frequency voltage induced across a secondary winding of said output transformer, a high frequency operation detector for detecting at least one of the high frequency voltage and the high frequency current and thus producing a high frequency operation detection signal, a controller for controlling said switching device of the high frequency generator in a feedback manner for a normal operation state in response to the high frequency operation detection signal applied thereto so that the high frequency operation detection signal becomes around a prescribed level, while controlling the switching device of the high frequency generator so as to carry out a first protection operation when the high frequency operation detection signal has changed to a second level or a second protection operation when an abnormal discharge control signal has been applied thereto, a no-load detector for detecting a no-load condition of the secondary winding of the output transformer and forcefully changing the high frequency operation detection signal supplied to the controller to the second level, and a current detector provided with a current detecting element for detecting a current flowing through the primary side of the output transformer and an impulse bypass capacitor connected in parallel with said current detecting element, for supplying a current detection signal to the controller.
This aspect of the invention defines an apparatus for detecting a no-load state and an abnormal discharge to correctly protect against them. For example, when a no-load state is detected, a first protection operation of reducing or reversibly suspending the high frequency output is carried out. On the other hand, when an abnormal discharge is detected, a second protection operation of unreversibly suspending the high frequency output is carried out. However, both the first and the second protection operations can be made to carry out a protection to reversibly suspend the high frequency output, as needed.
For the operations of detecting and protecting a no-load state, the first and second aspects of the invention can be employed. Moreover, for operations of detecting and protecting an abnormal discharge, the configuration of the third aspect of the invention can be employed. However, by making the third aspect of invention to detect a high frequency current by the no-load detector, the current detector used in this aspect of the invention can be shared with the abnormal discharge detector. Therefore, the third aspect of the invention can avoid a complication of circuitry. In this case, the no-load detector and the abnormal discharge detector can be provided with a diode for preventing an undesired signal superimposition between the detectors.
Moreover, the controller may be or may not be provided with the regulator IC with the shutdown function.
As this aspect of the invention can detect both the no-load state and the abnormal discharge to protect them, it is able to provide a useful lighting apparatus for the dielectric barrier discharge lamp.
A discharge lamp lighting apparatus according to a fifth aspect of the invention includes, a discharge lamp provided with a discharge vessel filled with an inert gas-dominated discharge agent and a pair of electrodes at least one of which is placed on the outer surface of said discharge vessel, a high frequency generator provided with a switching device for generating a high frequency voltage with a high frequency switching operation and an output transformer for outputting a high frequency voltage, for lighting the discharge lamp by supplying to the discharge lamp through a pair of electrodes with the high frequency voltage induced across a secondary winding of said output transformer, a high frequency operation detector for detecting at least one of the high frequency voltage and the high frequency current and thus producing a high frequency operation detection signal, a controller for controlling said switching device of the high frequency generator in a feedback manner for a normal operation state in response to the high frequency operation detection signal applied thereto so that the high frequency operation detection signal becomes around a prescribed level, while controlling the switching device of the high frequency generator so as to carry out a protection operation when the high frequency operation detection signal has exceeded a prescribed level, and a current detector provided with a current detecting element for detecting a current flowing through the primary side of the output transformer and an impulse bypass capacitor connected in parallel with said current detecting element, for supplying a current detection signal to the controller.
This aspect of the invention defines a configuration for carrying out a protecting operation by detecting an overcurrent.
If, for example, the primary winding of the output transformer has a large stray capacitance, an impulse occurs due to a transient oscillation which arises at an instant that the switching device has been turned ON. When such an impulse occurs, the overcurrent detector fails to work properly and thus resulting in an unintended protecting operation.
Accordingly, in this aspect of the invention, the impulse contained in the current detection signal is suppressed before the current detection signal is supplied to the controller. That is, the current detector is provided with a current detecting element and an impulse bypass capacitor. The current detecting element, which is comprised of a resistor with a low resistance, detects a current flowing in the primary side of the output transformer. Accordingly, the current detecting element is easily isolated, and the circuitry thereof is simplified. The impulse bypass capacitor is connected in parallel with the current detecting element. The term xe2x80x9cin parallelxe2x80x9d includes such a direct parallel connection fashion and an indirect parallel connection fashion in which a current detecting element is connected via a voltage divider. The impulse contained in the current detection signal is removed by bypassing through the impulse bypass capacitor. Thus, an impulse-free current detection signal is supplied to the controller.
Thus, in this aspect of the invention, even if an impulse due to a stray capacitance of the primary side of the output transformer is contained in the current detection signal, the overcurrent detector does not fail to work properly.
A discharge lamp lighting apparatus according to a sixth aspect of the invention is characterized in that the output transformer as defined in the first to fourth aspects of the invention has a multiplayer primary winding.
This aspect of the invention defines a configuration that the stray capacitance of the primary winding of the output transformer is reduced. That is, in order to reduce the stray capacitance, the number of turns of the primary winding is lessened. However, if only the number of turns is lessened, the inductor is reduced, so as to disturb a required voltage transform operation. However, the stray capacitance of the winding varies in proportion to a number of turns of adjacent winding. Accordingly, the number of turns of the primary winding of the output transformer is maintained to be a required numbers by making it a multi-winding, in addition, the number of turns of adjacent winding is lessened, so that the stray capacitance is remarkably reduced.
Further, in this aspect of the invention, the inductor on the primary side of the output transformer is preferable to be up to 30 mH. The number of layers of the primary winding may be two or more.
Since such an occurrence of the impulse due to a stray capacitance of the primary winding lowers according to this aspect of the invention, it is effective to prevent a malfunction of the abnormal detector for detecting abnormal condition such as an overcurrent.
A discharge lamp lighting apparatus according to a seventh aspect of the invention is characterized in that it is provided with a timer in addition to the first through sixth aspects of the discharge lamp lighting apparatus. Therefore, this aspect of the invention is characterized in that it suspends the protection operation of the controller for a predetermined period at the starting of the discharge lamp.
The timer is enough to start at a proper timing in the starting operation. For example, the timer can start in synchronization with the timing that the high frequency generator is turned ON.
Since a dielectric barrier discharge lamp is started by being supplied with a power of a high voltage and a high frequency, the abnormal discharge detector tends to work improperly due to the high voltage with a high frequency. Moreover, an abnormal discharge tends to occur along an outer surface of the discharge vessel due to the starting high voltage, before a normal dielectric barrier discharge occurs through the discharge agent in the discharge vessel. Therefore, there is a possibility of that an unstable phenomenon may transitionally occur for a predetermined period at the time of starting. In a discharge lamp whose lamp voltage is so increased to have a high output by relatively increasing a pressure of the discharge agent so as to increase the impedance of the lamp, there is a possibility of that such an unstable phenomenon may transitionally occur.
Since the timer in this aspect of the invention suspends the protection operation of the controller for a predetermined period at the starting of the discharge lamp, undesired protection operations due to a malfunction can be prevented.
A lighting apparatus according to an eighth aspect of the invention includes, a lighting apparatus main body, and a discharge lamp lighting apparatus as defined in the first to seventh aspects which is provided with the lighting apparatus main body.
This aspect of the invention is provided with a discharge vessel wherein a discharge agent which is made of inert gas as its key constituent is hermetically filled and a pair of electrodes at least one of which is placed on the outer surface of the discharge vessel. It is applied to any apparatus for the purpose of using emission of the discharge lamp that is connected to the output terminal of the discharge lamp lighting apparatus.
The term xe2x80x9clighting apparatus main bodyxe2x80x9d means a almost entire portion of the lighting apparatus except the discharge lamp lighting apparatus.
As the apparatus, there are for instance, a lighting equipment, an image readout device, a facsimile, a scanner or a copying machine which are installing the image readout device in, a back light device of a liquid crystal display, and an indicator on a car.
More particularly, in the discharge lamp according to this aspect of the invention, since at least one set of electrodes is placed on the outer surface of the discharge vessel, a configuration that a discharge light is derived through the slit left between the electrodes is easily adopted. Thus the discharge lamp is preferable for the image readout device or the back light device. However, if the outer electrode is made light-transmissive or the outer electrode defines therein a gap which allows a discharge light to pass therethrough, the discharge light is derived from the discharge lamp omnidirectionally. Such an omnidirectional construction is advantageous for designing a easy-to-use lighting equipment.